Variable condenser



June 18, 1929. c. P. sRocKwAY VARIABIJE CONDENSER K Filed May 6. 1922 INVENToR. 6dr/ f? Broc/ way BY 5ML l Patented June 18, 1929.

UNITED STATES 1,717,912 PATENT OFFICE.

CARL P. BROCKWAY, OF TOLEDO, OHIO, ASSIGNOR T0 ARCTURUS RADIO TUBE COM- PANY, 0F NEWARK, NEW JERSEY, A CORPORATION 0F DELAWARE.

VARIABLE CON DENSER.

Application led 'May 6,

This invention relates to improvements in variable condensers, which, while they may find utility in various electrical arts, have proven to be particularly applicable to radio work.

One of the objects of the invention is the provision of a simplified structure which may be produced at greatly reduced cost over the forms of variable condensers now in common use.

Another object is the provision of apparatus of this character which will permit the use of a solid dielectric of relatively high dielectric power, whereby the employment of a large number of condenser plates is made unnecessary.

Another object of the invention is the provision of gauging means which will enable the operator to set the condenser at any angle in either of two complete revolutions of the adjusting screw.

A further object is the provision in a condenser of this character, of means for mounting the adjustable plate which will retain it in position without appreciably interfering with its elasticity.

Still another object is the provision of means for preventing the body capacity of the operator from noticeably affecting the capacity of the condenser during adjustment of the latter.

Other objects, and objects relating to details of construction and economies of manufacture, will appear as I proceed with the description of that embodiment of the invention which, for the purposes of the present application, I have illustrated in the accompanying drawing, in which Figure I is a plan view of a condenser embodying my invention.

Fig. II is a cross-sectional view taken substantially upon the line II-II, Fig. I, and showing the condenser mounted upon an 1nstrument board.

Fig. III is a plan view of the condenser with the adjusting disc or cover removed.

Fig. IV is a fragmental, sectional view on the line IV-IV, Fig. III, showing one of the binding posts.

Similar reference characters refer to like parts throughout the views.

In order to car out the invention, it 1s necessary to provi e a shallow, circular receptacle for the condenser plates. As will be obvious, this receptacle may be formed 1n the 1922, Serial No. 558,976.

instrument board itself, but I prefer to employ a block 10 of suitable insulating material, having a circular rim 11, enclosing a circular recess adapted to receive a lower, fixed condenser plate 12, a dielectric sheet 13, preferably of mica, and an upper adjustable condenser plate 14. The adjustable plate 14 is bowed, while the fixed plate 12 is flat. The edges of the bowed plate which come nearest to the edges of the fixed plate are preferably extended outwardly beyond the edges of the fixed plate and are adapted to rest upon the dielectric sheet which is extended at these points for this purpose.

The block 10 is adapted to be mounted upon an instrument board indicated at 15 in the drawing. This is accomplished primarily by a bolt 16, having an elongated cylindrical head 17 bearing against the edges of a hole bored through the center of the block 10. Another hole is bored throught the instrument board to receive the bolt 16, upon the end of which is threaded a nut 18 for clamping the parts together. The head 17 may be made integral with the shank of the bolt 16 or otherwise, depending upon expediency in manu' facture.

The two binding posts may also be so constructed as to assist in fixing the condenser upon the instrument board. These binding posts are mounted preferably in countersunk holes in the block 10. As shown in Fig. IV, the beveled head of the post 19 is caused to draw the metal of the lower plate 12 closely down upon the walls of the countersink, forming a good electrical contact as well as a secure and rigid mounting of the plate upon the block 10. A threaded bushing 2O is set into the instrument board 15 and constitutes a securing nut for the binding post, while upon the end of the latter is threaded a binding nut 21 of conventional design.

The binding post 22 for the u per condenser plate 14 engages a narrow nger 23 integral with the plate and cut back into the plate as shown clearl in Fig. III, leaving that edge of the plate otherwise free to slide and rock as its adjustment is changed. The post 22 in addition anchors the dielectric 13. It passes through a threaded bushing 24 and is provided with a binding nut 25 similar in all respects to the bushing 20 and nut 21 on the post 19.

The head 17 on the central bolt 16 is thread.- ed as shown in Fig. II to receive a threaded bushing 26 mounted centrally in the knob 27 and adjusting disc 28, the latter titting rather closely within the receptacle formed Aby the rim 11, and thus constituting a cover for the receptacle to protect the parts therein mounted.

The periphery of the disc 28 is marked a shown in Fig. I, with any desired number of divisions in order to form a gauge by means of which the condenser may be set to have the capacity required for a given purpose. The range of adjustment may be made to include two complete revolutions; by marking the edge of the disc with a circle, as indicated at 29 in Fig. II. This circle isy always exposed to view during one revolution of the disc, and is hidden by the rim 11 during the second revolution.

I have found that it is advisable to ground the central bolt 16 to reduce the efect upon the condenser of the hand ofthe operator in turning the knob 27. I therefore connect the bolt 16 with binding post 22 by means of a thin, fiat conductor 30, where the condenser is designed to be used in acircuit in which that binding post is grounded.

The operation of the device will be obvious from the above description, it being understood that the adjustable plate 14 possesses a high degree of resiliency and isv normally bowed out centrally away from the lower plate 12. As the knob 27 is turned down, the central portion of the plate 14 approaches the dielectric 13, thus increasing the capacity of the condenser. Inasmuch as the edges of the bowed plate which are adjacent the fixed plate extend beyond the edges of the fixed plate, any movement of the bowed plate causes a greater variation of a capacity than would be the case if the edges of thebowed plate were even with the edges of the fixed plate, as the charge on the plates is concentrated at the nearest points.

I claim as my invention:

1. In apparatus of the class described, a pair of condenser plates separated by a solid dielectric, one of said plates being iiat and the other normally bowedoutwardly from the flat plate at the center, and means parallel with the iiat plate and extending beyond the bowed plate for causing said bowed plate to approach more or less closely a plane parallel with the flat plate, said bowed plate being normally in engagement with the dielectric at the edges thereof which are nearest said fiat plate, such engagement being made beyond the ends of said fiat plate.

2.,A condenser comprisin two metallic plates separated b a solid dielectric, one of said plates being at and the other being resilient and normally bowed away from the flat plate and having its ed es which come nearest to the iiat plate exten ing beyond the edges of said flat plate, and screw-threaded adjusting means parallel with said flat plate and extending beyond said bowed plate for causing said bowed plate to approach more or less closely a plane parallel with the iiat plate and a metallic connection between the adjusting means and one of the plates.

3. A condenser comprising two metallic plates separated by a solid dielectric, one of said plates being flat and the other being resilient and normally bowed away from the fiat plate and having its edges which come nearest to the fiat plate extending beyond the edges of said flat plate, screw-threaded adjustin g means parallel with said iat plate and extending beyond said bowed plate for causing said bowed plate to approach more or less closely a plane parallel with the iat plate, and a gauge comprising a circular scale and a pointer, one of which is mounted upon the screw-threaded adjusting lneans, for indicat' ing the different ldegrees of adjustment.

4. In a device of the class described, a circular insulating block provided with an upstanding rim, a pair of metallic condenser plates mounted within the rim and separated by a solid dielectric, one of said plates being bowed away from the other, and screwthreaded adjusting means for causing said bowed plate to approach more or less closely a plane parallel to the other plate, said means comprising a disc to close the opening within said rim.

5. In a device of the class described, a circular insulating block provided with an upstanding rim, a air of metallic condenser plates mounted within the rim and separated by a solid dielectrc', one of said plates bein bowed away from the other, screw-thread adjusting means for causing said bowed plate to approach more or less closely a plane parallel to the other plate, said means comprising a disc to close the opening within said rim, and a ring around the edge of said disc adapted to be covered by Said rim in part of the adjusted positions of said disc. n

6. In a device of the class described, a circular insulating block provided with an upstanding rim, a pair of metallic condenser `plates mounted within the rim and separated by a solid dielectric, one of Said plates being bowed away from the other, screw-threaded adjusting means for causing said bowed plate to approach more or less closelya plane parallel to the other plate, said means comprising a disc to close the opening within said rim, a gauge including a circular scale and a pointer, one mounted upon the disc and the other upon the rim, and a ring around the edge of the` said disc adapted to be covered by the rim after -the disc has been turned down one complete revolution.'

7. A condenser comprising two metallic plates separated by a solid dielectric, one of said metallic plates being resilient and normally bowed outwardly awayfrom the other plate at the middle, said resilient plate being formed with a relatively narrow finger at one side by means of which it is mounted, and means parallel with the other of said plates and extending beyond said resilient plate for causing said resilient plate to approach more 011 less closely a plane parallel with the other p ate.

8. A condenser comprising two metallic plates separated by a. solid dielectric, one of said metallic plates being resilient and normally bowed outwardly away from the other plate at the middle, said resilient plate being formed with a relatively narrow fm er at one side of and cut back into the plate, y means of which the plate is mounted, and means parallel with the other of said plates and extending beyond said resilient plate for causing said resilient plate to approach more or less closely a plane parallel with the other plate.

In testimony whereof I alli; my signature. 20

CARL P. BROCKWAY. 

